Pore structure of shale

页岩的孔隙结构

Fuel, Volume 143, 1 March 2015, Pages 467-475

Abstract: Pore connectivity is limited in shale formations, unlike in conventional reservoirs, for which cyclic void models, such as the regular-lattice model, are often used to represent the connectivity. In the cyclic models, the random assignment of throat sizes to lattice elements leads to a plateau-like variation of a capillary pressure with wetting phase saturation during a drainage displacement. Here, we develop acyclic void models in which the spatial distribution of throat sizes is not random. For certain spatial distributions these models yield a non-plateau-like drainage displacement. Such models thus provide more realistic representations of the void space in samples for which drainage experiments reveal the non-plateau-like trend of the capillary pressure versus saturation. Gas shales commonly show such a trend, and using the developed models, we predict the no-slip permeability of shale samples whose mercury intrusion capillary pressures curves were measured under confined boundary conditions. The predicted permeabilities are in good agreement with the lab measurements reported for these samples. Other models either fail to account for the non-plateau-like trend of the drainage as they adopt a random pore size distribution or they overestimate the no-slip permeability for saturated flow. The models developed here could have applications in other porous media whose drainage data do not exhibit a plateau-like variation.

Kerogen based characterization of major gas shales: Effects of kerogen fractionation

基于油母的主要气页岩表征：油母分馏的影响

Organic Geochemistry, Volume 78, January 2015, Pages 52-61

Abstract: Research into the origin and the mode of entrapment and expulsion of natural gas from unconventional plays requires the isolation and separation of kerogen in its purest and most intact form from the rock matrix. This study expands on the comparative analysis of the effects that isolation methods, conservative closed system versus conventional open system, have on kerogen’s elemental, isotopic and physical properties. Four major gas shales, including the Barnett, the Marcellus, the Haynesville and a Polish gas shale, were chosen. In addition, the Monterey shale, though not strictly a gas shale, was included to address the effects on sulfur rich, Type II-S kerogen.

Results indicate that the kerogen residues from the conventional open system method showed lower recovery and higher mineral content than those from the conservative closed system method. Differences were manifested in the elemental analysis data, where kerogens isolated using the open system method showed a significant deficit in the organic C, H, O, S and N material balance. Furthermore, the recovered residues show different sulfur content and δ34S composition, most likely attributable to differences in pyrite content. Nevertheless, the relative abundances of the various macerals in the kerogen residues from the same parent shale are not very different; neither was the bulk δ13C composition of the recovered residues. This is not particularly surprising, considering that in all the five cases examined in this study, the organic matter was fairly homogeneous.

Assessment of organic richness and hydrocarbon generation potential of Raniganj basin shales, West Bengal, India

印度孟加拉邦Raniganj盆地页岩有机物富集度及生烃潜力评估

Marine and Petroleum Geology, Volume 59, January 2015, Pages 480-490

Abstract: High energy prices and severe energy shortage has led shale gas to become the focus of study and exploration in many countries. India, like many other countries around the world with shale gas potential recognizes the strategic importance of developing its shale gas resources. For the purpose of shale gas assessment, the authors have selected sixty six borehole shale samples of different formations from different parts of Raniganj basin, West Bengal, India. Rock eval pyrolysis and total organic carbon (TOC) analysis and petrographic characterization of the shales were carried out. Shales from Barakar (Lower Permian), Barren Measures (Upper Permian) and Raniganj Formation (Upper Permian) are marked by ‘good’ to ‘excellent’ TOC content, input of type III organic matter and are capable of generating oil and thermogenic gas upon thermal cracking. Igneous intrusives (dykes and sills) in the formations occurring in and around the areas of Sitarampur (Si) and Kulti (Ku) in western part of the basin might have resulted in cooking of the shales, increasing their maturities (estimated vitrinite reflectance, VRo) as indicated by the Barren Measures shales of shallow depths from the above mentioned areas. Majority of the samples are marked by low oxygen index (OI) values.

A comparison of shale permeability coefficients derived using multiple non-steady-state measurement techniques: Examples from the Duvernay Formation, Alberta (Canada)

基于多功能非稳态测量技术的页岩渗透率系数比较：加拿大阿尔伯塔省Duvernay地层实例研究

Fuel, Volume 140, 15 January 2015, Pages 371-387

Abstract: Matrix permeability, while an important control on fluid flow in unconventional reservoirs, is difficult to measure in the laboratory. There are now multiple methods for laboratory determination of permeability for shales, but little consensus on the appropriate method for permeability measurement. Each technique is based on different physical principles and utilizes reservoir samples at different scales. The combination of sample size and preparation and measurement conditions can lead to a wide range in permeability estimates, creating confusion for recipients of the data. In this work, we compare different non-steady state methods for determination of gas permeability in low-permeability Canadian shales and provide insight into the causes of permeability variation. Further, we analyze and discuss the effects of different controlling factors including porosity, pore-fluid content, mineralogy and effective stress on permeability.

Gas permeability measurements were conducted on low-permeability (shale) samples from the Duvernay Formation (Alberta, Canada) using three different methods: profile (probe), pulse-decay and crushed-rock permeability techniques. The analyzed samples differ in total organic carbon (TOC) content, pore network characteristics (porosity, pore size distribution), pore-fluid content (“as-received” and cleaned/dried) and mineralogy. Profile (probe) and crushed-rock permeability measurements were performed on samples in the “as-received” and cleaned/dried conditions. Pulse-decay measurements were conducted on samples in the cleaned/dried state. Helium pycnometry/expansion measurements were performed using “as-received” and cleaned/dried samples under unconfined and controlled “in situ” effective stress conditions....

The observed discrepancies between permeability values derived from the various non-steady-state techniques is rationalized in terms of sample size, treatment, stress-state and physical principals of measurement. The combined use of these methods is however recommended to provide insight into the controls of sample heterogeneity at sub-cm scales, which is particularly important for shale samples.

Enhanced oil recovery in shale reservoirs by gas injection

通过注气提高页岩气藏油采收率

Journal of Natural Gas Science and Engineering, Volume 22, January 2015, Pages 252-259

Abstract: The current available technique to produce shale oil and gas condensate is through primary depletion using horizontal wells with multiple transverse fractures. The oil recovery factor is only a few percent. There is a big prize to be claimed in terms of enhanced oil recovery (EOR). Because gas price is low and oil price is high, maximizing liquid oil production from gas condensate reservoirs becomes shale producers' top interest.

This paper provides the status of enhanced oil recovery (EOR) in shale oil and gas condensate reservoirs by gas injection. It starts with the discussion of possible EOR options in shale reservoirs. For the gas injection option, the huff and puff mode is compared with the gas flooding mode. Different modes of water injection in shale oil reservoirs are also compared. The discussion and comparison show that gas injection is more feasible in shale reservoirs than waterflooding and any other EOR methods. The rest of the paper focuses on review of gas injection in shale reservoirs, which covers the following.

Shale gas produced water treatment using innovative microbial capacitive desalination cell

用新型微生物电容脱盐燃料电池处理页岩气生产产生的废水

Journal of Hazardous Materials, Volume 283, 11 February 2015, Pages 847-855

Abstract: The rapid development of unconventional oil and gas production has generated large amounts of wastewater for disposal, raising significant environmental and public health concerns. Treatment and beneficial use of produced water presents many challenges due to its high concentrations of petroleum hydrocarbons and salinity. The objectives of this study were to investigate the feasibility of treating actual shale gas produced water using a bioelectrochemical system integrated with capacitive deionization—a microbial capacitive desalination cell (MCDC). Microbial degradation of organic compounds in the anode generated an electric potential that drove the desalination of produced water. Sorption and biodegradation resulted in a combined organic removal rate of 6.4 mg dissolved organic carbon per hour in the reactor, and the MCDC removed 36 mg salt per gram of carbon electrode per hour from produced water. This study is a proof-of-concept that the MCDC can be used to combine organic degradation with desalination of contaminated water without external energy input.